The present invention relates to a mechanical timepiece which operates by using as a driving source mechanical energy generated when a mainspring is released. In addition, the present invention relates to an electronic controlling type mechanical timepiece in which a portion of the mechanical energy of the mainspring is converted into electrical energy, and a rotation controlling means is operated by the electrical energy in order to control a period of rotation.
An electronic controlling type mechanical timepiece shown in FIG. 16 is known, in which a mainspring used as an energy source drives a wheel train, and electrical power is generated by a generator rotated as a result of receiving the rotational motion from the wheel train in order to drive an electronic circuit which controls the period of rotation of the generator, whereby the wheel train is braked to regulate the speed.
In the electronic controlling type mechanical timepiece, rotation of a movement barrel 1 in which a mainspring 1a is accommodated is transmitted to a second wheel 6 to which a minute hand (not shown) is mounted, after which the rotation is transmitted successively to a third wheel 7, a fourth wheel 8, a fifth wheel 11, a sixth wheel 12, and ultimately to a rotor 13 of the generator. A second pinion wheel 90 to which a second hand (not shown) is attached meshes only with the third wheel 7, so that it is situated outside a torque transmission path extending from the movement barrel 1 to the rotor 13. In order to reduce unsteady movement of the second hand caused by backlash between the third wheel 7 and the second pinion wheel 90, a second regulating spring with a suitable structure is sometimes provided.
In such an electronic controlling type mechanical timepiece, the speed of the rotor 13 is stably regulated, and, when the wheels 6, 7, 8, 11, and 12, and the second pinion wheel 90 are formed with ideal shapes, the second pinion wheel 90, that is, the second hand moves exactly at a constant speed of 1 rpm.
However, there are variations in the shapes of the wheels 6, 7, 8, 11, and 12 and the second pinion wheel 90, so that, when, in particular, the second pinion wheel 90 with a small pitch circle is decentered from its axis of rotation, the rotational speed of the second pinion wheel 90 will not be 1 rpm, causing the second hand to shift.
To overcome this problem, the pitch circle size of the second pinion wheel 90 may be made larger. However, in such a case, since the speed-increase ratio (which is, in general, 60) from the second wheel 6 to the fourth wheel 8 needs to be maintained, a teeth-shaped module of the second pinion wheel 90 is made large, making it necessary to either make the third wheel 7 larger or increase the speed-increase ratio between the second wheel 6 and the third wheel pinion. This reduces the meshing efficiency.
FIG. 15 illustrates a graph showing the measured shift angles of the hand of the conventional electronic controlling type mechanical timepiece. In the timepiece, since a large speed-increase ratio in which the second pinion wheel 90 rotates nine times during the time the third wheel 7 rotates once is set, the pitch circle of the second pinion wheel 90 becomes small, so that the decentering of the second pinion wheel 90 greatly affects the shift angle of the hand. It has been confirmed that, during the time the second pinion wheel 90 rotates nine times, the second hand is greatly shifted by an angle in the range of from xe2x88x921.2xc2x0 to +4xc2x0 from its normal position in a circumferential direction thereof.
The electronic controlling type timepiece uses the mechanical energy of the mainspring as a driving source, so that the larger the width of the mainspring (that is, the width of the timepiece in the thickness direction thereof), the longer the timepiece will continue operating.
However, forming the mainspring with a large thickness increases the thickness of the timepiece, thereby preventing the formation of a thin timepiece.
This problem not only exists in electronic controlling type mechanical timepieces, but also in conventional mechanical timepieces in which a wheel train is driven by a mainspring.
Accordingly, it is an object of the present invention to provide a timepiece which makes it possible to reduce the amount by which a second hand is shifted, and which can continue operating for a longer time without increasing the thickness of the entire timepiece.
A timepiece according to one aspect of the present invention includes a speed-regulating device for regulating a speed of rotation of a wheel train, in which a mainspring serving as an energy source drives the wheel train,
wherein, of wheels of the wheel train, a wheel to which a second hand is mounted is disposed so that torque of the mainspring is transmitted to the speed-regulating device, the wheel to which the second hand is mounted including a pinion and a gear provided on a same axis of rotation, and being disposed so as not to overlap the mainspring when viewed in a plane.
In this invention, the wheel to which the second hand is attached includes a pinion and a gear, so that, by engaging a wheel disposed towards the mainspring and the pinion, and engaging this gear with a next gear (disposed towards the speed-regulating device), the diametrical dimension from the center of rotation of the wheel to which the second hand is attached to a portion where it engages the next gear can be made large without changing the speed-increase ratio from the mainspring side. Therefore, even if the wheel to which the second hand is attached gets decentered, the effects of the decentering at the center-of-rotation side becomes small, so that the amount by which the second hand gets shifted is reduced.
In addition, since the wheel to which the second hand is attached is disposed so as not to overlap the mainspring, the width of the mainspring can be correspondingly increased, so that the torque of the mainspring becomes large even if the thickness of the entire timepiece is not increased, thereby increasing the length of time the timepiece continues operating.
Due to the above, the above-described object is achieved.
The speed-regulating device may be constructed so as to regulate the speed of rotation of the wheel train by controlling a period of rotation of the generator by an electronic circuit driven by electrical power generated by the generator to which a rotational force from the wheel train has been applied.
Although, as in a mechanical timepiece, the speed-regulating device may comprise an escapement, the speed of the wheel train can be more precisely regulated when the electronic controlling type structure of the present invention is used.
It is desirable that the wheel to which the second hand is mounted and a gear of a barrel drum which accommodates the mainspring overlap each other when viewed in a plane.
In this structure, since the outside diameter of the gear of the barrel drum can be made large, the speed-increase ratio between it and a wheel at the wheel train side which engages the gear becomes large. Thus, the winding down of the mainspring when the train wheel is rotating at a constant speed can be slowed down, thereby increasing the length of time the timepiece continues operating.
A timepiece according to another aspect of the present invention in which a mainspring serving as an energy source drives a wheel train, and in which a speed of rotation of the wheel train is regulated by controlling a period of rotation of a generator by an electronic circuit driven by electrical power generated by the generator which has received a rotational force from the wheel train,
wherein, of wheels of the wheel train, a wheel to which a second hand is mounted is disposed so that torque of the mainspring is transmitted to the generator, the wheel to which the second hand is mounted including a pinion and a gear provided on a same axis of rotation; and
wherein the wheel train is disposed so as not to overlap a coil of the generator when viewed in a plane.
In the present invention, since the wheel to which the second hand is attached includes a pinion and a gear, the amount by which the second hand shifts can similarly be reduced.
In addition, since the wheel train is disposed so as not to overlap the coil, the number of windings can be increased based on a corresponding increase in the diametrical dimension of the coil, so that the axial length of the coil, and, hence, the magnetic path length becomes shorter. Consequently, iron loss such as hysteresis loss or eddy current loss occurring when a magnetic field is generated in the coil is reduced, making it possible to operate the timepiece with a smaller amount of mainspring energy, so that the timepiece can continue operating for a longer period of time.
Due to the above, the above-described object is achieved.
It is preferable that a pitch circle diameter of the gear of the wheel to which the second hand is mounted be at least 1.5 mm.
This is because, when the pitch circle diameter of the gear of the wheel is less than 1.5 mm, the effects of decentering cannot be made sufficiently small, so that effective reduction in the amount by which the hand shifts cannot be expected when the pitch circle diameter is less than 1.5 mm.
It is preferable that a barrel drum which accommodates the mainspring be supported in a cantilever fashion to a main plate.
In such a case, the barrel drum (or the barrel arbor) is supported by the main plate alone, so that, when a wheel train bridge is disposed so as not to interfere with the barrel drum by, for example, not forming a portion of the wheel train bridge at a location which corresponds to that of the barrel drum, the wheel train bridge can be disposed closer to the main plate side, making it possible to make the timepiece thinner. On the other hand, instead of bringing the train wheel bridge closer to the main plate, the width of the mainspring can be made large in order to increase the length of time the timepiece continues operating.
A wheel which engages the wheel to which the second hand is mounted and which is disposed towards the generator in a mainspring torque transmission system path may have one end side axially supported by a wheel train bridge and the other end side axially supported by a second wheel bridge disposed between the main plate and the wheel train bridge.
In this case, it is not necessary to axially support the shaft of the wheel located towards the generator by the main plate and the train wheel bridge, so that the wheel is disposed so as not to interfere with, for example, the minute hand wheel (that is, the second wheel). Therefore, it is possible to reliably transmit the torque of the mainspring to the rotor by engaging the gear of the wheel to which the second hand is mounted with a next wheel, without increasing more than necessary the size of the gear of the wheel to which the second hand is attached.
Here, the wheel disposed towards the generator in the mainspring torque transmission system path may be an idle wheel which does not increase or decrease in speed. In this case, the wheel is thinner than the wheel including the pinion and the gear.
A wheel located closer to the mainspring than a wheel which engages a rotor of the generator in the mainspring torque transmission system path may have one end side axially supported by the second wheel bridge disposed between the main plate and the train wheel bridge and the other end side axially supported by the main plate.
In this case, it is not necessary to axially support the wheel located towards the mainspring by the main plate and the train wheel bridge, so that the wheel train can be disposed in a smaller space without the axis of rotation of the wheel being interfered with, making it possible to make the timepiece smaller.